The present invention relates to the field of jet pumps.
The present invention is particularly, but not exclusively, applicable in the field of fuel tanks for motor vehicles.
Still more precisely, the present invention can be applied in transferring fuel between various chambers of a multichamber fuel tank, or for filling a reserve bowl from which fuel is drawn by a fuel pump or any other fuel supply device.
Examples of fuel suction devices based on jet pumps are shown in documents DE-A-3 915 185, DE-A-3 612 194, and DE-A-2 602 234.
Although known suction devices based on jet pumps have given good service, they nevertheless do not always give satisfaction.
In particular, it has been observed that the flow injected into the jet pump, and corresponding to fuel being returned from the engine or to a fuel bypass taken from the outlet of the pump, can sometimes present fluctuations in pressure and/or flow rate that are large so that it is difficult to match the characteristics of the jet pump, and in particular to avoid large back pressures appearing at the inlet of the jet pump if the section of its outlet bore is too narrow for the injected flow rate and/or pressure.
Various proposals have been made in an attempt to eliminate that drawback.
Thus, for example, document DE-A-4 201 037 proposes a plunger core carried by a spring-biased membrane and placed inside the nozzle, upstream from its outlet bore, such that the plunger core moves back in the event of pressure increasing, thereby increasing the free section of the nozzle bore. In a variant, document DE-A-4 201 037 proposes making the body of the nozzle itself in the form of an element that is deformable relative to a fixed plunger core, likewise to adapt the section of the outlet bore to the injected pressure.
In its French patent application No: 96 11739 filed on Sep. 26, 1996, the Applicant has itself proposed a jet pump in which the nozzle which receives the injected flow is made up of a bore comprising a plurality of lips of elastic material that are adapted do that the section of the bore varies depending on the injected pressure and flow rate.
Other known solutions consist in placing a discharge valve upstream from the nozzle or the inlet for the injected flow of the jet pump, which valve is suitable for opening when the injected pressure exceeds a rated threshold for the valve. Nevertheless, those solutions present the drawback of losing a portion of the fluid that is bypassed via the valve, such that this portion of the fluid is not injected into the nozzle.
An object of the present invention is now to propose a novel and improved jet pump.
In the context of the present invention, this object is achieved by a jet pump comprising a nozzle and a core mounted to move relative to the outlet bore of the nozzle and downstream therefrom. According to an advantageous characteristic of the present invention, the core is of right section that increases going away from the outlet bore of the nozzle.
In a variant embodiment in accordance with the present invention, the core is provided with a through longitudinal channel that forms an auxiliary nozzle. The operation of this variant embodiment is described below.